The invention pertains to a device and a method for encapsulating an element within a microcavity made on a support. The invention also pertains to a microcapsule incorporating this encapsulation device.
The term “microcavity” herein designates a cavity whose width is at most 1 or 5 mm and whose height is at most 1 mm or 500 μm.
The term “element” herein designates a microcomponent as well as a material such as a liquid or a gas.
Microcomponents are electromechanical microsystems known as MEMS (microelectromechanical systems) or NEMS (nanoelectromechanical systems) as well as other microcomponents such as electronic, optical and optoelectronic microcomponents or biochips. Integrated circuits also come under the term “microcomponents”.
Microcavities and microcomponents differ from cavities or macroscopic components also by their method of manufacture. These microcavities and microcomponents are made by using the same collective manufacturing methods as those used to make microelectronic chips. For example, microcavities and microcomponents are made out of wafers, for example wafers made of monocrystalline silicone or glass, machined by photolithography and etching (for example DRIE or deep reactive ion etching) and/or structured by epitaxial growth and deposition of metallic materials.
Through these manufacturing methods, the microcavities and microcomponents generally have machined parts in which at least one of the dimensions is of the order of one micrometer. The dimension of the order of one micrometer is generally lower than 200 μm and for example ranges from 1 to 200 μm.
It is very often necessary to house an element inside a microcavity in order to insulate it and protect from the external environment. To this end, there are various known encapsulation devices. These known devices comprise an encapsulation membrane capable of forming at least one part of the microcavity.
For example, an encapsulation device can be created by using an encapsulation method known as “thin film packaging” (TFP). This is a collective method of encapsulation and uses techniques commonly used to make microcomponents. To make an encapsulation device using the TFP method, is it necessary especially to:
make the microcomponent on a support,
deposit a sacrificial layer on the microcomponent,
deposit the encapsulation membrane on the sacrificial layer,
pierce release holes in the encapsulation membrane to discharge or remove the sacrificial layer,
remove the sacrificial layer by means of the release holes, and
plug the release holes to shut the microcavity created by the removal of the sacrificial layer.
In a method of this kind for making the encapsulation device, it is necessary to pierce holes in the encapsulation membrane. Then, it is necessary to plug these holes, and this may pollute the interior of the microcavity with, for example, residues of hole-plugging material.
Another type of encapsulation device is made by attaching a cap to the support. The cap is machined by the same techniques as those used to make the microcomponent. The cap is machined independently of the support to be encapsulated. Then, the cap is assembled on the support to form the microcavity in which the element to be encapsulated is received. This assembling operation is a complex one. For example, it requires that the cap be precisely positioned relative to the element to be encapsulated and then that the cap be sealed to the support.
The prior art presented here above is described in greater detail in the following document D1, the contents of which is herein incorporated by reference: J. L. Pornin & al, <<Wafer Level Thin Film Encapsulation for BOW RF MEMS>>, CEA-LETI, 57th ECTC (Electronic Component and Technology Conference), June 2007.